1. Field of the Invention
The present invention relates to an apparatus for solidifying a casting to create a directionally solidified or single crystal casting and, more particularly, to an apparatus which is capable of introducing a cooling spool into a casting mold and withdrawing the casting mold from a stationary heating chamber.
2. Related Art
Solidifying molten materials, such as molten metal, in a mold cavity to create a directionally solidified or single crystal casting is known. FIGS. 1a and 1b illustrate a conventional apparatus 10 for producing a casting. An example of this is disclosed in U.S. Pat. No. 4,969,501. The apparatus 10 includes a heating chamber 12 defining an interior volume 16 which is heated via heating elements 14. A plurality of casting molds 20 are disposed in an annular array on a vertically movable chill plate 22. The molds are supported in and removable from the interior volume 16 by the movable plate 22. The movable plate 22 is vertically displaced by column 24. More particularly, the casting molds 20 may be removed from the interior volume 16 by displacing the plate 22 in the direction of arrow A (FIG. 1b) while the heating chamber 12 remains stationary.
Unfortunately, apparatus 10 produces directionally solidified or single crystal castings having less desirable material properties due to lower thermal gradient during casting. A thermal baffle or heat sink is not introduced into an interior region of the casting mold apparatus during the withdrawal from the heating chamber 12 to selectively absorb radiant heat being supplied from the molds 20. Indeed, there is very little if any control of thermal gradients at the molds 20 to obtain directionally solidified castings.
In order to obtain a directionally solidified or single crystal casting, a casting mold must be removed from a heating chamber using special procedures.
FIGS. 2a and 2b show another conventional apparatus 50 to produce a directionally solidified or single crystal casting. An example of this is disclosed in U.S. Pat. No. 5,778,961. The apparatus 50 includes a heating chamber 12 defining an interior volume 16 for receiving an annular array of casting molds 20. The casting molds 20 surround and define an interior space 21. The molds are disposed on an annular chill plate or disk 30 which includes a central aperture 31. A thermal baffle or heat sink 34 us shaped and sized to pass through the aperture 31 in the plate 30, and the baffle is movable vertically upward in the direction of arrow C (FIG. 2b) with respect to the plate 30 by its supporting column 36. In particular, the thermal baffle 34 may be moved into the interior space 21 by moving the column 36 upward, and vice versa. The radiation baffle 19 is disposed below the open end of the heating chamber 12.
As illustrated, the casting molds 20 are maintained in a substantially fixed position and height with respect to a floor 32. The casting molds 20 are removed from the interior volume 16 of the heating chamber 12 by raising the heating chamber 12 in the direction of arrow B (FIG. 2b). Thermal baffle 34 may be moved into interior space 21 while the heating chamber 12 is moved. Of course, the chamber 12 can remain stationary and the molds may be moved out downwardly.
The thermal baffle 34 serves as a heat sink to absorb radiant heat from the molds 20 such that the molten material within the molds 20 is solidified directionally by a thermal gradient defined from the heating chamber 12 to the thermal baffle 34. The thermal gradient is a function of the temperature difference and relative positions of the heating chamber 12 and the thermal baffle 34. Therefore, the higher is the temperature of the heating chamber 12 and the greater is the magnitude of heat that the thermal baffle 34 can absorb, the higher are the thermal gradients obtained.
Since the thermal baffle 34 may be moved relative to the molds 20, the thermal gradient may be controlled to some extent. Unfortunately, apparatus 50 only maximizes the thermal gradient and, therefore, does not satisfactorily provide the thermal gradient control needed to produce castings of different geometries and configurations or single components having substantially complex geometries and still result in desirable directionally solidified or single crystal articles.
Moreover, when a component is manufactured in a fixed thermal gradient system as shown in FIG. 2a-2b, the constant thermal gradient applies to the entire article and is normally not optimized over respective areas of the article. Constant, and particularly high thermal gradients may cause increases in casting scrap because hot tear prone alloys may crack as a result of thermal stresses due to the high thermal gradient.
Accordingly, there is a need in the art for a directionally solidified or single crystal casting apparatus which provides a high degree of control of thermal gradients when withdrawing casting molds from a heating chamber.